Charles McDonald, 64, had just delivered 8,000 gallons of propane to Atlas Castings & Technology when his tanker exploded Saturday shooting debris 150 feet high and spreading fire to two nearby storage tanks, the Seattle Times reported. Three other workers received minor injuries.

Authorities were unclear whether the fire started inside the foundry or near the tanker, said assistant fire chief Dan Crotty.

“What’s clear is that there was a leak and it found an ignition source,” Crotty said.

It will take several days for investigators to work methodically from the perimeter of the damage to the center, the Tacoma (Wash.) News Tribune reported.

Crews have yet to determine how to remove the propane remaining in two large storage tanks, which still pose a potential hazard, the Tribune reported.